Nowadays, the use of mobile devices, e.g. personal digital assistants, portable computers and mobile phones, for wireless communication purposes is widespread. Furthermore, new applications for these devices emerge rapidly. In many of these new applications, services are provided which relate to functionality to the end user of the mobile device based on its location, so called Location Based Services (LBS). Services include, for example, providing navigational support, providing a local weather forecast, or searching for a nearby restaurant.
Depending on the type of service to be provided, different methods of determining the location of the mobile device can be applied. Some services require very accurate locations, while others only need to know the location in a more general fashion.
Well-known methods of determining the location of a mobile device are based on the location of a base station of the radio cell the mobile device is camped on. In these methods, localization may, for example, be based on cellular base station identifiers sent by cellular base stations in the network. If the mobile device knows the geographic location of the base stations corresponding to the base station identifiers, it can determine its position. The determination may be done by assuming that the position of the mobile device coincides with the closest base station, by calculating the position by using a triangulation technique based on positions of surrounding base stations, or by using other techniques known to a person skilled in the art.
Because the coverage area of a cellular base station is relatively large, the accuracy of the localization will be relatively low. This may become an issue for future mobile device applications, in particular if these applications involve LBS that need a very accurate location determination. Especially in buildings, the location determination can be improved, e.g. to determine on which floor the mobile device is located.
One way to improve the accuracy of the determined position is to base the location determination on wireless access points, e.g. access points used in a wireless local area network (WLAN). Wireless access points generally have a smaller coverage area than cellular base stations. Furthermore, wireless access points are often located in buildings. Based on determining cell identifiers of wireless access points, Service Set Identifier (SSID) in WLAN, a more precise location determination is possible. A method of determining a location of a mobile device based on wireless access points has been described in U.S. Pat. No. 6,968,194. A wireless access point that is equipped to be used in such a method has for example been described in European patent application 1802154.
Generally, the coverage of a network of wireless access points is not continuous, but concentrated in so called hotspots. As a result, in some geographical areas, the density of wireless access points is relatively low. Consequently, in these areas, a localization of a mobile device based on a method as described in U.S. Pat. No. 6,968,194 may be less accurate than desired.
In a patent application filed in parallel to the present application by the present applicant, it is proposed to determine a location of a mobile device based on available communication units within a predetermined geographical area. The available communication units may support different types of radio technology. Although such an arrangement improves the accuracy of determining a location of a mobile device, a further improvement may be accomplished.
The inventors of the invention described in this application have recognized that the reliability of a communication unit position may vary widely. Some communication units will be installed by consumers, which may not be familiar with all aspects of such an installment. Consequently, erroneous position determination is more likely to occur. On the other hand, the positions of other communication units, especially communication units that are installed by an experienced provider, are generally highly reliable.
Additionally, the inventors have recognized that a communication unit with a large coverage area may, if used in location determination calculations, lead to a less accurate determining of a position as compared to a communication unit with a smaller coverage area. Furthermore, the accuracy of a communication unit position may also depend on the type of coordinates used, e.g. a communication unit position expressed in Global Positioning System (GPS) coordinates may express the position more accurately than a communication unit position expressed in the form of a postal code or a postal address.
Thus, an improvement of localization of a mobile device in a communications network is desired.